1. Field of the Invention
The present invention relates to a system and method for determining desired engine torque for a powertrain having a transmission with a torque converter.
2. Background Art
Internal combustion engines having electronic throttle control (ETC) typically determine a driver-demanded torque based (at least in part) on accelerator pedal position. The driver-demanded torque is typically interpreted as the wheel torque or net torque available to the system to accelerate the vehicle. However, the engine controller can only influence the combustion or indicated torque produced by the engine by controlling the throttle valve position, ignition timing, and fuel injection timing and quantity. To provide the desired output shaft or wheel torque, the indicated or combustion torque produced by the engine must take into account any torque multiplication or reduction provided by the drivetrain, in addition to various losses and engine/vehicle accessory loads. For automatic transmission applications, the torque converter multiplication should be considered. However, the inventors herein have recognized that torque multiplication of the torque converter is dependent upon a variety of operating parameters of the engine and transmission and may be difficult to determine precisely, particularly during transient conditions, using prior art strategies.
One prior art strategy uses a well-known torque converter relationship between torque ratio and speed ratio to calculate the desired engine combustion torque (or torque converter impeller torque) based on a desired wheel torque and corresponding torque converter turbine torque. This strategy essentially iteratively solves the torque converter equations, which may result in a slow or sluggish response to a driver demand for an increase in output shaft or wheel torque for moderate acceleration, particularly when a vehicle is driving away from a full stop. In addition, this strategy may not adequately account for inertia-based torque loads which occur during transient operation resulting in a sluggish response and poor drivability.
An object of the present invention is to provide a system and method for determining a desired engine torque during unlocked torque converter operation from a desired turbine torque to improve the response to an increase in driver-demanded output shaft or wheel torque.
In carrying out the above object and other objects, features and advantages of the present invention, a system and method for controlling a multiple cylinder internal combustion engine include determining a driver-demanded torque, determining a target engine speed to deliver a desired torque converter turbine torque corresponding to the driver-demanded torque based on a torque converter model, determining a first engine torque based on the target engine speed, determining a second engine torque to accelerate the engine speed from a current speed to the target engine speed, and controlling the engine to deliver the sum of the first and second engine torques.
In another embodiment of the invention, a system and method for controlling a multiple cylinder internal combustion engine coupled to a transmission via a torque converter having a torque converter impeller selectively fluidly coupled to a torque converter turbine include determining a driver-demanded torque, determining a first engine torque based on the driver-demanded torque and a steady-state model of the torque converter, determining a second engine torque based on a current engine speed and a target engine speed, wherein the second engine torque is based on a speed ratio of turbine speed and impeller speed, and controlling the engine to deliver the sum of the first and second engine torques.
The present invention provides a number of advantages. For example, the present invention accounts for inertia-based torque loads that occur during transient operation to provide a more responsive control for part-throttle accelerations, particularly for vehicle launch, i.e., when driving away from a complete stop. In addition, the present invention provides desirable drivability in a full authority electronic throttle control (ETC) system. As known, full authority ETC systems may result in reduced losses and increased fuel economy as compared to mechanical throttle and pedal follower systems.
The above advantages and other advantages, objects and features of the present invention will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.